1. Field of the Invention
This invention relates to an improvement in a high pressure discharge lamp apparatus such as a high pressure mercury lamp apparatus, a high pressure sodium lamp apparatus, or a high pressure metal-halide lamp apparatus. The present invention especially concerns an improvement in a high pressure discharge lamp apparatus of the type comprising a high pressure discharge tube, a current limiting device, for instance a choke coil and a pulse generator for impressing pulses across the discharge tube for lighting the tube with a lamp voltage nearly equal to a power source voltage.
2. Description of the Prior Art
Generally, in a conventional high pressure discharge lamp apparatus, a current limiting device such as a choke coil and a discharge tube are connected in series across a power source.
In the abovementioned type of the high pressure discharge lamp apparatus, a voltage of the power source should be maintained over 1.5 times a voltage of the discharge tube for preventing an extinction of ignition in the tube.
In order to improve the abovementioned shortcoming, an improvement has been devised such that the discharge lamp is ignited each cycle by a circuit, for example, of FIG. 1. The conventional apparatus of FIG. 1 comprises a specially designed current limiting device 2' having an additional coil 202, besides the ordinary choke coil 201 which is connected in series to the discharge tube 3 across the power source 1. A capacitor 203 and a voltage-responsive switching device 5 are connected in series to said additional coil and the series connection of these is connected across both terminals of the discharge tube 3. The additional coil 202 and the capacitor 203 form a resonance circuit 204. In this circuit, pulse current is produced in the series circuit of the resonance circuit 204 and the switching device 5 during the while lamp current is not flowing, and therefore, high voltage pulses are impressed across the discharge tube by means of the choke coil 201. In such reignition circuit of self-excitation type the lamp current has a zero-current period in each cycle, and therefore, the apparatus has the shortcomings that:
(i) The input current has distorted waveform having a considerable components of third and fifth higher harmonic waves, thereby the apparatus becomes a noise source, PA1 (ii) Apart from the fluorescent lamp where such self-excitation type reignition is effective and extinctions rarely occur, in case of operating a high pressure discharge lamp a use of such self-excitation type reignition is liable to distinction since the existence of zero-current period causes an increase of reignition voltage.
Therefore the self-excitation type reignition is not suitable for the high pressure discharge lamp apparatus.